FIG. 1 schematically shows a piezoelectric linear motor of the prior art. As shown in the drawing, piezoelectric ceramics 2 are stacked upon one another. As further shown in the drawing, a shaft 4 is coupled to the rightmost piezoelectric ceramic 2″ of the stacked ceramics 2. The leftmost piezoelectric ceramic 2′ of the stacked ceramics 2 is fixed to a supporting part 6 of an instrument or a device to which the piezoelectric linear motor is installed.
The reference numeral 8 indicates a driving circuit that is electrically connected to the piezoelectric ceramics 2 for applying a voltage thereto. The piezoelectric ceramics 2 expand when the voltage is applied and contract when the voltage is removed. The shaft 4 moves axially according to the expansion or contraction of the piezoelectric ceramics 2.
A moving element 9 is mounted to the shaft 4 such that the moving element 9 frictionally interacts with the shaft 4. When the shaft 4 moves relatively slowly, the moving element 9 moves linearly together with the shaft 4 by the friction therebetween. However, when the shaft 4 moves relatively fast, since the friction-acting time is shortened, the moving element 9 does not move by inertia. Rather, only the shaft 4 moves axially. Since the process of adjusting the moving speed of the shaft 4 by controlling the voltage wave applied to the piezoelectric ceramics 2 is already well known in this art, the explanation thereof is omitted herein.
As the low-speed forward movement (as indicated by arrow a) and the high-speed backward movement (as indicated by arrow b) of the shaft 4 are repeated, the moving element 9 gets to move forward. However, as the low-speed backward movement and the high-speed forward movement of the shaft 4 are repeated, the moving element 9 gets to move backward. An object to be moved, such as a photo lens, is fixed to the moving element 9.
However, the above prior art piezoelectric linear motor is limited in the displacement of the moving element 9 by the expansion or contraction of the stacked piezoelectric ceramics 2, thus making it difficult to displace the moving element 9 to a target position within a short time with a large driving force.